The present invention relates to a process for preparing intermediates useful in the preparation of benzazepines having activity as selective D1 receptor antagonists.
U.S. Pat. No. 4,973,586 discloses fused benzazepines, and in particular the compound known as SCH 39166, having the structure ##STR4## as selective D1 antagonists useful in the treatment of psychoses, depression, pain and D1 dependent neurological disorders. Methods for preparing such compounds are also described therein.
Berger, et al, J. Med. Chem., 2, 1913-1921 (1989), discloses a process for preparing SCH 39166 comprising acid promoted cyclization of a compound of the formula (1) to give a 1:1 mixture of cis and trans benzazepines (cis-2 and trans-2, respectively). Compound trans-2 is then converted to racemic compound I via a multi-step procedure. Compound I is resolved via its di-O,O'-p-tolyltartrate salt and hydrolyzed with HBr and HOAc to give SCH 39166. ##STR5## The prior art process suffers from several shortcomings. It is inefficient, producing a 1:1 mixture of cis and trans benzazepines in the cyclization step. In addition, conducting the resolution step at a late stage of the synthesis is very costly and adds further inefficiency. Therefore, it was desirable to develop a chemically efficient and cost effective process for preparing SCH 39166 of high optical purity. It was also desired that the resolution be performed at an early stage of the process or that the chiral centers be introduced using inexpensive chiral starting materials, thereby avoiding the need for resolution.